On the mechanism of the cyanide-insensitive alternative pathway of respiration in fungi and higher plants and the nature of the alternative terminal oxidase.

In connection with investigations on the mechanism of action of the systemic fungicide carboxin a new hypothesis was developed on the mechanism of the cyanide-insensitive pathway of respiration, which is widely distributed in fungi und higher plants, and on the nature of the alterative terminal oxidase. Based on own experimental results which are in concordance with the properties of the alternative pathway described in the literature, it is assumed that the nonheme-iron-sulfurprotein (FeSPp) of the succinodehydrogenase, which is located on the main route of the cytochrome mediated respiration, is the alternative terminal oxidase itself. This property seems to be based on the ability for autoxidation in some organisms where the Fe-atoms are oxygenized and reach the maximal coordination number of 6. By this mechanism it is explainable that carboxin which also attacks the normal electron flow at the FeSPp of the succinodehydrogenase is able to inhibit simultaneously under certain circumstances the cyanide-insensitive respiration organisms sensitive to carboxin.